Does the mass of sample loaded affect faecal haemoglobin concentration using the faecal immunochemical test?

Abstract

Background Quantitative faecal immunochemical tests (FIT) for haemoglobin are being used for colorectal cancer (CRC) screening for asymptomatic populations and are being indicated as a suitable test to rule out CRC in symptomatic populations. Faecal samples are typically collected by patients using a probe attached to the cap of a device which is inserted into a collection device into the preservative buffer, passing through a collar to remove excess sample: this process has potential for pre-analytical error. This study investigates whether faecal haemoglobin concentration (f-Hb) results are affected by the mass and method of sample collection. Methods Faecal samples with detectable f-Hb were loaded into collection devices from four manufacturers using increasing masses of sample. The f-Hb in the device buffer was measured using the relevant analyser. The results from the minimum recommended load were compared with results of 'sample overloading'. Results The variation in the faecal mass added to the probe (overall CVs: EXTEL HEMO AUTO-MC Collection Picker 300%, OC-Auto Sampling Bottle 3 237%, SENTiFIT pierceTube 264%, Specimen Collection Container A 250%), was more than the variation in f-Hb (respective overall CVs: 62%, 35%, 47%, 39%). The mass of faeces added to the probes increased significantly ( P < 0.0001 for all four devices), but the f-Hb did not increase significantly (EXTEL HEMO AUTO-MC Collection Picker P = 0.6820, OC-Auto Sampling Bottle 3 P = 0.9368, SENTiFIT pierceTube P = 0.7551, Specimen Collection Container A P = 0.6864). Conclusion The mass of sample loaded onto the probe did not impact the f-Hb significantly using all four tested devices.

The Effect of the Variability in Fecal Immunochemical Test Sample Collection Technique on Clinical Performance

“…Some brands of FIT promote collection of feces from multiple sites and, although this was not shown to alter diagnostic accuracy compared with sampling from just one site (19), instruction for multi-site sampling might reduce the risk of under-sampling. Our results, and that of a published in vitro study that loaded up to 74 mg on to the collection device probe (10), confirm that over-sampling does not adversely affect diagnostic accuracy and clinical outcomes, provided that at least 10 mg is collected and inserted into the device.…”

“…However, factors related to the collection itself may also influence the diagnostic accuracy and subsequent clinical performance, such as quantity of feces collected in the device. Results from previous studies on the effect of the addition of different quantities of fecal samples are inconsistent, with one study showing that the addition of feces to Hb-spiked buffer changed the measured f-Hb (9), whereas another study showed that varying the quantity of Hb-spiked feces collected in the FIT devices did not significantly change f-Hb (10).…”

Assessment of the analytical performance of point-of-care faecal immunochemical tests for haemoglobin

“…The iO (CV range 0.9–15.5%) uses the OC-Sampling Bottle 3 which previous work has shown has a well-designed internal collar to remove excess faeces; this study showed the mass of faeces loaded on to the probe did not affect the concentration of Hb captured by the device. 14 The QuikRead go (CV range 2.6–17.5%) has a similar design with a tight fitting collar to remove excess faeces. The Cube has a collar but it is not as tight as the other two devices which could lead to increased variation in the amount of faeces in the buffer.…”

Does visually over-loaded HM-JACKarc collection device impact faecal haemoglobin results?

“…In our previous study we demonstrated that artificially overloading of samples didn’t impact the faecal haemoglobin concentration (f-Hb) significantly. 3 In this study we further investigated with patient samples whether there was an association between the total mass of the collection device and corresponding f-Hb. We also investigated if faecal material that remained adhered to the dimple(s) of the device affected f-Hb.…”

“…This is consistent with our previous findings that loading of excess faeces around the dimple(s) of the collection device and higher up had no significant impact on the f-Hb. 3…”